This is a group of ex-Russian Orthodox faithful who changed jurisdictions within Orthodoxy, which happens all the time as all our Churches are in communion with one another. This is a far cry from what you wrote:

Makes sense the Antiochian Church was under the Russian Patriarchate.

That is patently false, the Antiochian Church was never under the Russian Patriarchate. Some Antiochians were formerly under the Russian Orthodox Patriarch and are now Antiochians.